In recent years, electric utilities have been receiving applications from Independent Power Producers (IPP) seeking interconnection agreements to connect to their electric grid. In order for an IPP to connect to the electrical grid system, an isolation and protection scheme has to be implemented to prevent islanding from occurring. An islanding situation occurs when there is a break on a section of the grid between a substation and a distribution generation (DG) facility. When this happens, the connected DG may face a number of problems:                Islanding creates a potential hazard for utility line-workers and the public by causing a line to be energized by the DG although the line is assumed to be disconnected from the main power grid.        The distributed generator may become overloaded when it is forced to power the isolated line.        The DG can be damaged when reconnected to the main power grid after being islanded since the DG is unlikely to be synchronized with other DG sites in the system at the instant of reconnection, and out-of-phase reclosing can inject massive current to the DG.        While being in the islanding situation, the DG could produce incorrect voltage and frequency to other power users connected to the power line near the DG, which can damage equipment at the users.        
The IEEE 1547 standard requires that DG sites go offline within 2 seconds from detection of an islanding condition. A Transfer Trip (TT) command must be signaled in order to cause the tripping (opening) of a recloser or circuit breaker at the DG site so that the DG site is physically disconnected from the electrical power grid. This requirement can be implemented in a number of different signaling methods. Traditionally, copper telephone lines, wireless radio and fiber-optics have been used for signaling. However, telephone lines installed in substations are costly because they require expensive ground potential rise equipment. Radio solutions using unlicensed 900 MHz spectrum do not reach far enough to be useful except in very rare situations where the substation is very close to the generator and no other reclosers are installed on the feeder. Fiber based solutions are also costly and require a longer installation process.